Extended Conditional Access (XCA) is a system for protecting digital encoded audio/video (A/V) content during transmission and storage. Under the XCA system, content of economic value is scrambled, or encrypted, to prevent unauthorized access. XCA allows recording of scrambled content, but does not permit descrambling of content that is not legitimate. Legitimate content is that which is an original or otherwise authorized by the copyright owner, for example. Of course, descrambling refers to the process of decryption. Since non-legitimate content is not descrambled, it cannot be viewed.
A distinct characteristic of the XCA architecture is the notion of conditional access (CA) and local protection. CA specifies access to protected content, such as programming. Removable security devices perform security related functions. Content of economic value is delivered using a CA service. For example, digital satellite systems scramble video content and the descrambling keys for mass distribution to their subscribers. Some subscribers may decide to purchase the content in which case they are supplied with the necessary keys to recover/obtain the descrambling key. Those subscribers choosing not to purchase the content are not provided access to these keys. In XCA terminology, this is the process of CA.
XCA systems use a return channel to receive authentication of the local keys and identities that are used for accessing content. This creates a problem in that most devices need to have a return path method of some sort to make this work.
An improved method for authenticating keys and identifiers used to access otherwise protected content in XCA and other systems which exhibit conditional access is desirable.